Muscle hypertrophy due to compression of the L5 nerve root

Neurogenic hypertrophy of the calves is well known as a result of S1 radiculopathy. Here we report a case of a discogenic compression of the L5 nerve root followed by a hypertrophy of the ventral compartment of the lower leg and to a lesser extent of the calf muscles.

Case report: A 49-year-old man suffered from transient sciatica with radiating pain on the left side two years earlier. Further on he noticed a painless progressive enlargement of the left lower leg.

Findings: Physical examination revealed a marked enlargement of the left tibialis anterior muscle, the peroneal muscles and the left calf. Nerve conduction studies of the sural and peroneal nerve and H-reflex of the tibial nerve were within normal limits. Electromyography showed evidence of abnormal spontaneous activity with fibrillation potentials and complex repetitive discharges of the tibialis anterior muscle, the peroneal muscles, the gluteus medius muscle and the soleus muscle, but not of the gastrocnemius muscle. A lumbar myelogram revealed compression of the L5 root on the left side. On axial T2-weighted images of the lower leg, intermediate signal intensity with fine linear streaks of high intensity was seen within the left soleus muscle corresponding to tiny fatty bands. Axial T1-weighted images showed high signal intensity within the peroneal muscles and extensor digitorum longus muscle corresponding to fatty infiltration, but no enhanced gadolinum uptake. Cerebral spinal fluid analysis and creatine kinase were within normal range. Muscle biopsy revealed a marked hypertrophy and prevalence of type I fibres, prominent degenerative changes and remarkable regenerative activities of type II fibres but no mononuclear cell infiltration.

Conclusions: Besides S1 nerve root also L5 nerve root compression must be considered in a painless hypertrophy of the lower leg. The affected muscles in our case showed a typically L5 distribution including the soleus muscle which can be partially innervated by the L5 nerve.

A thorough examination of the lumbar spine including electromyography, magnetic resonance imaging, and in selected patients a myelogram is needed to work up patients with localized muscle hypertrophy of the lower leg before an other differential diagnosis, e.g. a focal myositis is considered.